Magnetic structure in relation to the magnetic field induced ferroelectricity in Y-type hexaferrite Ba$_{2−x}$Sr$_{x}$Zn$_{2}$Fe$_{12}$O$_{22}$

Thakuria, Pankaj

Book	FZJ-2017-07074

Magnetic structure in relation to the magnetic field induced ferroelectricity in Y-type hexaferrite Ba$_{2−x}$Sr$_{x}$Zn$_{2}$Fe$_{12}$O$_{22}$

Thakuria, P. (Corresponding author)FZJ*

2017
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-250-4

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich. Reihe Schlüsseltechnologien / Key Technologies 151, 180 S. (2017)

Please use a persistent id in citations: http://hdl.handle.net/2128/15715

Abstract: This thesis consists of in depth study of spin structure of magnetoelectric Y-type hexaferrite Ba$_{2−x}$Sr$_{x}$Zn$_{2}$Fe$_{12}$O$_{22}$ system. Magnetoelectric and multiferroic materials are of high interest from information technology point of view, but traditional mechanism of magnetism and ferroelectricity makes it rare to observe both in single phase materials. One of the most widely studied non conventional mechanism where cross coupling of magnetism and ferroelectricity takes place in non-collinear spin systems is spin driven ferroelectricity by inverse Dzyaloshinskii-Moriya (IDM) mechanism or spin currect mechanism (SC). The spin frustration leading to non-collinear spin arrangements also leads to low magnetic ordering temperature hinders room temperature realization of magnetoelectric coupling effect. Hexaferrite systems are an answer to high temperature magnetoelectric behavior in single phase materials. Y-type hexaferrite with composition Ba$_{2−x}$Sr$_{x}$Zn$_{2}$Fe$_{12}$O$_{22}$ was the first hexaferrite to show magnetoelectric behavior, where a 2-fan planar spin structure was proposed, not compatible with the magnetic field (H) induced ferroelectricity by IDM/SC mechanism. In depth investigation of the spin structure and its relationship with macroscopic field driven ferroelectricity was the central point of this thesis. The widely accepted spin structure of Y-type hexaferrite is a spin block model with large (L) and small (S) spin blocks, collinear in spin arrangements inside the blocks but between the blocks arrangements changes from collinear to spiral depending upon the chemical composition. With change in the Sr content in the composition Ba$_{2−x}$Sr$_{x}$Zn$_{2}$Fe$_{12}$O$_{22}$ spin structure was reported to change from collinear to in plane spiral in earlier studies. The change in spin structures were easily visible in magnetization curves, when magnetic field was applied perpendicular to c-axis. In three samples with x=1.4,1.18 and 0.72 grown by flux methods, our refinement of single crystal x-ray diffraction data shows that Sr substitution causes local distortion and change in occupancies of Zn in the tetrahedral site which happens to be in the spin block boundary, accompanying a change in the Zn/Fe-O bond length. We speculate that the cumulative effect of local distortion, change in occupations of Zn and bond length change changes the superexchange interaction near the block boundary changing the spinstructure. [...]

Note: RWTH Aachen, Diss., 2017

Contributing Institute(s):

Research Program(s):

Experiment(s):

Appears in the scientific report 2017

Database coverage:
Creative Commons Attribution CC BY 4.0